The present invention relates to a heat exchanger for a nuclear reactor.
More specifically the invention relates to a heat exchanger for fast neutron nuclear reactors cooled by a liquid metal such as sodium in which exchangers are located in the main tank of the reactor. Such exchangers, commonly called intermediate exchangers, ensure a heat transfer between the primary fluid which is most often constituted by liquid sodium and a secondary fluid which is also liquid sodium, whereby said secondary sodium within the tank exchanges its calories with a water-vapour circuit to produce electric power.
More specifically the invention relates to sodium-sodium exchangers of the straight tubular type in which these tubes are mounted between a secondary fluid supply chamber and a secondary fluid discharge chamber. The group of tubes is in the form of an annulus arranged between an outer ferrule and an inner shaft for supplying the supply chamber. Moreover, in this type of generator the primary liquid metal is supplied and discharged by two open orifices, respectively in the upper part and lower part of the outer ferrule between the supply and discharge chambers.
In the case of integrated reactors and as will be better understood by referring to the attached FIG. 1 which will be described hereinafter, the heat exchanger is suspended by its upper portion on a slab which seals the reactor vessel. Considerable masses are involved because this exchanger has, for example, an exchange length of 8 meters, the corresponding volume being filled by liquid sodium. In addition, the sodium is kept under a slight pressure to ensure its circulation, so that it applies dynamic stresses to the different parts of the exchanger. Finally, there are significant temperature gradients in the different parts of the exchanger, leading to thermal expansion problems, which in turn cause mechanical stresses within the exchanger.
FIG. 1 shows, in vertical sectional form, a fast neutron reactor cooled by a liquid metal and of the integrated type.
In the greatly simplified FIG. 1 it is possible to see the concrete enclosure 2, whose upper part is sealed by slab 4. The main vessel 6 is suspended on the slab, whilst flooring 8 supports the reactor core 10. An inner vessel 12 with a recess 13 separates the hot sodium from the cold sodium. Intermediate exchangers, such as 14, are suspended on slab 4. Each exchanger sealingly traverses the recess 13. A supply orifice 56 (positioned above the recess) and a discharge orifice 58 (positioned below the recess) ensure the circulation of the primary sodium within the exchanger. Each exchanger has a group of straight or substantially straight tubes, the term "substantially" meaning that the tubes can have over a portion of their length and particularly at their ends helically shaped regions which give the tubes a greater flexibility. There are also primary pumps such as 15 suspended on slab 4. These pumps have supply orifices 16 and their outlet is connected by tubes such as 18 to the support 20 of the reactor positioned below the core 10. Secondary fluid, which is also usually sodium, circulates within exchanger 14.